The present invention relates to hose clamps and more particularly, to hose clamps having a biasing portion integrally formed in the clamp.
Hose clamps are used to secure flexible conduits onto fittings by applying radially inward compressive forces onto the conduits for frictionally securing the conduits onto the fittings. Particularly in the automotive industry, hose clamps play an important role in securing flexible hoses onto the engine block and like components.
There are a number of types of hose clamps: (1) Wire or strip band, clamped by screw; (2) Strip band, clamped by deformation of a portion of the band (Oetiker and Keystone types); (3) Wire or strip spring types, clamped by spring forces where the wire or strip is deformed into a spring ring of smaller diameter than the hose so that when the clamp is installed over the hose a pattern of radially inwardly directed forces tend to squeeze the hose. All of these types of clamps are commonly used and vary considerably in effectiveness and cost to manufacture.
In general, the optimum clamp possesses the following features: low cost; uniformly inwardly radially directed forces to compress a hose onto a male tubular element to which the hose is being connected; a wide band for exhibiting a large peripheral "footprint" to reduce unit loading forces on the hose surface so that the hose material is least damaged by the inward forces; a means of assuring that the clamping force is sufficient and yet the force is not excessive; the clamp is suitable for a number of different methods of closing, tightening or cinching with or without tools; manufacturable from materials that may be treated to retard corrosion or are not sensitive to corrosion; and visual inspectability to assure that the clamp is correctly installed or torqued, if a threaded closure is used.
The hose clamp of the present invention, disclosed herein, moves the industry closer to this optimum goal. The present invention employs a novel spring concept for providing a method for overcoming the functional drawbacks of the presently available hose clamps.
The following is a description of the primary functional factors which must be satisfied in clamping a flexible hose to a nipple. Also, listed are the many disadvantages of existing hose clamps.
If it were possible to inexpensively manufacture flexible hoses with very close wall thickness, inside diameter control, and to manufacture mating nipple with close tolerances, at low cost, then the clamping problem would be reduced to merely producing a strip ring having a closely controlled inside diameter in its fully closed position and crimping or bolting the clamp to fix the strip ring onto the hose in the fully closed position. Unfortunately, high cost prevents making male nipples and flexible hoses having the close tolerances necessary to make this possible. Tolerances of cast nipples and hose wall thickness may have circumferential variations of over 3/16 inch on a hose that is installed onto a 5/8 male nipple. With this being the case, there are essentially the following choices:
(a) Close the clamp band to a diameter such that the smallest outside diameter hose is adequately clamped. If this is done, then the material of the hose is severely over stressed at the larger end of the hose outside diameter range. This alternative is generally not used because it causes premature failure of the hose.
(b) To accomodate the diameter range, screw "draw-in" type clamps are used, however, these types of clamps depend on torquing the screw down to produce proper inward forces. These types of clamps are commonly used, but have several disadvantages in controlling the inward forces exerted by the clamp. One disadvantage is the variation of frictional characteristics between the threaded members. It is important that the variations such that the friction be large enough to prevent the screw from loosening, yet not have a variable effect on the torque, which is the means by which proper clamping force is controlled. Other disadvantages are controlling wrenching torque (the human or automatic wrench repeatability factor), controlling "cold flow" of the hose material which "flows" away from the compressed area under the clamp over a period of time. The "cold flow" is why screw type hose clamps must be periodically tightened to maintain proper retention; and why most new hose installations should be "retorqued" a month or two after installation. The inability to quickly and accurately inspect whether or not the clamp is properly tightened is also a disadvantage. While a torque wrench may be used to insure proper torque, this is seldom done and such means is subject to the above mentioned difficulties.
To insure proper tightening of screw type clamps, the clamp must be tightened significantly more than is desired. The tightening compensates for "cold flow", causing higher inward forces to be present than a desirable compression range when first installed, and resulting in lower inward forces to be present after "cold flow" has taken place. During the initial higher than acceptable compression period, the hose is rapidly degraded and its life is significantly shortened.
(c) Use a formed spring wire or band ring having a diameter smaller than the outside diameter of the flexible hose on which it is to be installed. At first, such a configuration appears to be a good solution, however, further investigation indicates that this is not the case. Generally, these types of clamps have their wire ends by-pass each other by a distance sufficient to prevent the round hose shape from merely acting to cause skidding open of the clamp in response to inward forces produced between the ends of the clamp and the portion of the ring diagonally across from the ends. A tighter bend radius, in the portion of the ring diagonally across from the ends, compensates for "no-force" contribution existing at the ends area of the ring. This "no-force" contribution requires approximately twice the force to be exerted from this diagonally across area to produce the inward forces at right angles to the area diagonally across from the ends area which, in turn, produces non-uniform inward forces. The wire clamp provides a very narrow "footprint" which produces very high unit loading on the hose material which, in turn, shortens the life of the hose. This "footprint" problem is avoided by using a circular strip spring clamp having the strip bent into a ring so that the strip width is increased, increasing the footprint, and reducing hose damage. The inward force non-uniformity is still present, only the "footprint" has been improved.
(d) Strip band type clamps that are cinched together over the installed diameter may also be used. These types of clamps may be closed with special tools that limit the closing force to accomplish some amount of under/over cinching control. Disadvantages with these types of clamps are variations in metal thickness of the strip; heat treat temper of the metal; and variations in the bending and forming of the metal which is to be deformed in order to cinch the clamp closed. Efforts to obtain a set pull together force during cinching are almost completely defeated by these factors. Since the clamp cannot be completely closed, as previously discussed, there exists a major risk of substantial damage to the hose with these clamps.
Efforts to obtain ideal hose clamps have resulted in several patents. The following patents illustrate the state of the art.
German Patent No. 3,018,383 illustrates a clamp which may be applied to a conduit which clamps the hose in a manner to prevent leakage.
U.S. Pat. No. 1,779,806, issued Oct. 28, 1930, discloses a clamp which may be readily applied to a conduit which clamps the hose in a manner to prevent leakage even through excessive high fluid pressures. To this end, the well known open ring clamp of any type used in securing a rubber hose, or the like, to a metal tube, is provided with a resilient, contractible, and expenseful clamping member that is interposed between the rubber hose and the open ring clamp.
U.S. Pat. No. 1,823,139, issued Sept. 15, 1931, discloses a clamp comprising a strap of bendable metal adapted to be wrapped around a pipe or bar. The strap has one long edge having a series of notches and a clevis device adapted to embrace two overlining sections of the strap when so wrapped and extended into the notch in each section.
U.S. Pat. No. 3,324,234, issued June 6, 1967, discloses a clamp for making a connection with cables, rods, hex bars, and other conductive structures having generally circular cross sections. The clamp consists of a metal band with contact legs based along the longitudinal edges. When applied, the contact edges on each side of the connector exert a constant force against the object to be connected. This force is developed by the use of laterally extending resilient segments at the end of which are disposed the contact legs. The connector is provided with a tab and slot arrangement so it can be quickly fastened around the objects to be connected.
Accordingly, it is an object of the present invention to overcome the disadvantages of the above art. The present invention provides the art with a clamp having a large footprint area for applying substantially equal radial forces around the circumference of a flexible conduit. The present invention eliminates the above explained torque dilemma. Also, the present invention eliminates uneven forces provided at the connection ends of the clamp.
The new and improved hose clamp of the present invention includes a flat elongated metallic strip having a pair of end portions. A biasing portion is integrally formed from the elongated strip between the two end portions. Bending of the strip material is not required to achieve the spring response of the biasing portion. The biasing portion provides the strip with the ability to be stretched along the strip length direction and with resilient characteristics in the axial direction. A mechanism secured on the end portions enables removable fastening of the ends to one another, or the ends may be formed enabling locking of the ends to one another without the use of auxilary fasteners, or separate parts.
Generally, the flat elongated strip is formed from a strip of sheet metallic material. The biasing portion may be formed in the strip by a stamping/blanking process to remove material from the elongated strip, forming a serpentine configuration in the strip.
Also disclosed is a method of manufacturing the clamp of the present invention. The method includes providing a flat elongated metallic strip having two ends; forming a biasing portion in the elongated strip between the ends; and affixing or forming the means for fastening the ends to one another onto the ends of the elongated strip. Further, the forming may include stamping the elongated strip such that the integral serpentine configuration is formed between the ends of the strip, in the strip, in a manner to control the spring response characteristics of the biasing portion.
Further, the disadvantages and considerations of (a-d), above, enable one skilled in the art to appreciate the novelty and advantages gained by the serpentine strip spring clamp. The serpentine strip spring is formed by removing material from the strip band. By removing material from a strip of a given length, the resulting formed strip has a serpentine shape with a lesser width but with a longer length. The strip thickness also determines the strength of the spring in extension or stretch. The length of the serpentine is related to the extension the spring will provide under a given pulling force. For example, using 0.020 or 0.025 inch thickness strip, a spring may be produced which will stand a pull of several hundred pounds without failing. This is generally 10 to 100 times the pull force that can be achieved by bending these materials to produce a spring. Forces of this magnitude are more than adequate to produce the desired force for a given hose clamp. The "spring constant" (force divided by unit extension) is controlled by the serpentine length and material thickness, which relates to the original strip width and length as explained herein.
The serpentine configuration may, if properly dimensioned, yield a spring constant which is derived from several quite different deformations of the material. In the case of a hose clamp, it is desirable to have a large spring constant to initially provide a minimum inwardly directed oompressive force as the clamp is initially closed. This is derived by deforming the serpentine across its wide dimension. Once this initial force is achieved, it is desirable to have further closing of the clamp (extension of the spring) shift into a lower spring constant mode so that a lower force results from contimued closure. This is achieved by dimensioning the serpentine so that deformation begins to occur across the stock thickness. Since the stock thickness is less than the stock width, a lower spring constant is achieved during this mode. This accomodates the normal hose/nipple tolerances.
The user chooses a clamp by deciding the desired force range which is optimum between the inside diameter and outside diameter limits of the installed hose; the axount of hose material cold flow that will result (which is much less than conventional clamps since an "over force" is not necessary and a large "footprint" is still achieved); and selects the cost efficient combination of strip material thickness and spring constant for the intended circumference situation. By using the combination spring constants, the pull difference between the smallest installed hose outside diameter and largest installed hose outside diameter is easily brought within the acceptable compression range of the hose material.
The disclosed method of making a spring clamp enables positive closing of the clamp to a known position. This closing eliminates the human variability of the closing operation, and enables straight forward inspection of the clamp to determine if the clamp has been closed or not.
Reviewing the features for an optimum clamp and comparing them to the serpentine strip spring clamp, the following is found. Low cost--in its simplest form a serpentine clamp may made from a band that is about 1/2 inch longer than the circumference of the outside circumference of the hose to be clamped. The strip width generally is between 7/16 to 3/4 inch wide for normal hose situations but may be wider for exceptional hose situations. In its simple configuation, requiring a tool to stretch and set the band, the clamp is a single component, stamped from a strip of 0.020 inch thick metal, for example.
Assuming that the band of the clamp will slide on the surface of the hose, as occurs in all band clamps, each portion of the clamp produces a radial inward force which is substantially identical, except for the 1/4 inch portion where the band lock overlaps. This overlap area will produce the same force, have the same "footprint" area, but the orientation of the footprint is not the same as the rest of the serpentine when the lower costing single wrap configuration is used.
The present invention assures that the clamping force is sufficient and yet not excessive, as previously explained. Generally, it is the most reliable of all clamps in this requirement.
The present invention is suitable for a number of different closure or cinching methods. The closures may be used with or without tools, as shown in the various figures, and even a no tool, swing-over-center to lock latch may be effectively used and inexpensively manufactured. Also, the clamp of the present invention may be manufactured from materials that other clamps may be manufactured from. The present invention enables easy inspection of the closure because of the go--no go type decision.
From the following description and claims taken in conjunction with the accompanying drawings, and other objects, the advantages of the present invention will become apparent to one skilled in the art.